Doctor Carrington provides health and medical services to the agents of the intelligence organization known as the Railroad. He is also Desdemona's right-hand man.
Following the Switchboard incident, the doctor holds the second highest leadership position in the organization, though he relates that this has not much impact. He is easily exasperated and irritated, though he claims this to be because of the Railroad's numerous setbacks and losses. The doctor also expresses displeasure about Desdemona's tendency to send agents on dangerous missions to gather intelligence when said intel is already more or less known, but he usually keeps these thoughts to himself.
Having Curie as your companion leads to humorous dialogue of her asking Carrington at what university he studied medicine, much to his exasperation. Further dialogue between the two includes inquiries regarding current publications about medicine.
When the Sole Survivor gives his prototype rescued from the Switchboard during Tradecraft, you might be confronted by Carrington. The Sole Survivor may then ask him "Is there someone you like?". Preston Garvey will dislike this question and interrupt them saying "We're not here to make friends".